The importance of sputter-coated glass layer systems for achieving solar management properties in architectural windows and doors is now well established in commerce. In addition, the importance of using such layer systems in insulating glass units (known as "IG" units in the art) is equally well established. Examples of this latter use include double and triple paned windows and doors made up of at least two panes of glass sealed at their peripheral edges-to form an insulating chamber therebetween. Such chambers, in this respect, are often filled with a gas other than air, such as argon.
Important to the acceptance of such IG units in the marketplace are the following characteristics which relate directly to the sputter-coated layer system employed:
1) the desired amount of visible transmittance coupled with an acceptable level of infrared radiation reflectance;
2) a non-mirror-like appearance;
3) a color appearance which is either neutral or falls within an acceptable range of shades of a non-objectionable color;
4) resistance to weathering or other chemical attack, often referred to as "chemical durability"; and
5 ) resistance to abrasion (often referred to as "mechanical durability") during handling, particularly during the various steps necessary to produce an IG window or door from two or more sheets of glass, at least one of which has been pre-sputter-coated with the aforesaid layer system.
In addition to these physical characteristics, the coating system employed must be economical to produce. If it is not, the ultimate product, such as in an IG unit, may become so expensive as to inhibit demand.
It is well-known in the art that these desired characteristics often conflict when attempting to achieve them, and that, therefore, trade-offs often become necessary. For example, achievement of acceptable levels of transmittance or IR (infrared) reflection may have to be at the expense of durability (either chemical or mechanical, or both). In other trade-offs, undesirable colors and mirror-like windows (or doors) become unavoidable. In still further trade-offs, cost of production becomes a significant factor. Such problems create a need in the art for a new sputter-coated layer system which can achieve a better balance among these characteristics.
In U.S. Pat. No. 5,344,718 there are disclosed various excellent sputter-coated layer systems which achieve acceptably low values of emissivity (E), and thus are properly classified as a family of "Low-E" systems (i.e. a family of high IR reflectance coatings as defined below). In addition, such coating systems, as a family, generally exhibit durability characteristics which approach or equal those of pyrolytic coatings and thus are quite acceptable. Still further, these coatings, particularly in their preferred embodiments, exhibit high visible transmittance. At the same time they also exhibit a reasonably neutral color, ranging somewhat into the green side of blue which is, however, reasonably masked by the level of reflectance achieved to thereby appear substantially neutral. In addition, their visible reflectance characteristics are below 20% and thus avoid an undesirable mirror-like appearance when viewed from either the inside or outside when used, for example, as a window or door.
The family of layer systems disclosed in U.S. Pat. No. 5,344,718 employs various layers of Si.sub.3 N.sub.4 and nickel or nichrome to sandwich one or more layers of IR reflecting metallic silver between them, in a selected order, thereby to achieve the desired end properties. The entire disclosure of this patent, including the "BACKGROUND" section thereof is incorporated herein by reference.
Generally speaking this prior patent ('718) achieves its unique results by the use of a system comprised of five or more layers wherein from the glass outwardly the system comprises:
a) an undercoat layer of Si.sub.3 N.sub.4 ; PA1 b) a layer of nickel or nichrome; PA1 c) a layer of silver; PA1 d) a layer of nickel or nichrome; and PA1 e) an overcoat layer of Si.sub.3 N.sub.4. PA1 a) a layer of Si.sub.3 N.sub.4 having a thickness of about 450 .ANG.-600 .ANG.; PA1 b) a layer of nickel or nichrome having a thickness of about 7 .ANG. or less; PA1 c) a layer of silver having a thickness of about 115 .ANG.-190 .ANG.; PA1 d) a layer of nickel or nichrome having a thickness of about 7 .ANG. or less; PA1 e) a layer of Si.sub.3 N.sub.4 having a thickness of about 580 .ANG.-800 .ANG.; and, wherein PA1 when the glass substrate has a thickness of about 2 mm-6 mm the coated glass substrate has a visible transmittance of at least about 70%, a normal emissivity (E.sub.n) of less than about 0.07, a hemispherical emissivity less than about 5.5 ohms/.sub.sq. and has the following (E.sub.h) of less than about 0.075, a sheet resistance (R.sub.s) of reflectance and color coordinates wherein the glass side characteristics are; PA1 R.sub.G Y, about 12 to 19 PA1 a.sub.h, about -3 to +3 PA1 b.sub.h, about -5 to -20 PA1 R.sub.F Y, about 8 to 12 PA1 a.sub.h, about 0 to 6 PA1 b.sub.h, about -5 to -30 PA1 when viewed from outside: PA1 when viewed from inside:
When the system consists essentially of these five (5) layers, the following thicknesses are generally employed:
______________________________________ Layer Range (approx.) ______________________________________ a (Si.sub.3 N.sub.4) 400.ANG.-425.ANG. b (Ni or Ni:Cr) 7.ANG. or less c (Ag) 95.ANG.-105.ANG. d (Ni or Ni:Cr) 7.ANG. or less e (Si.sub.3 N.sub.4) 525.ANG.-575.ANG. ______________________________________
When, in this prior patent ('718), more than five layers are employed, such as when two silver layers are employed, the system from the glass outwardly usually includes the following layers:
glass/Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4, and the total thickness of the silver remains the same (e.g. 95 .ANG.-105 .ANG.) such that each layer of silver itself is only about 50 .ANG., to make up the total.
While such systems as disclosed in this prior '718 patent constitute a significant improvement over then existing prior art systems, particularly those discussed in the "BACKGROUND" section of that patent; nevertheless, there remained room for improvement in the characteristic of "emissivity". For example, in the systems of the '718 patent, normal emissivity (E.) was generally less than or equal to about 0.12 while hemispherical emissivity (E.sub.h) was generally less than about 0.16. However, in practice, the lower limits realistically achievable were generally, for E.sub.n about 0.09 and for E.sub.h were about 0.12. Achievable sheet resistances (R.sub.6) in this respect were generally from about 9-10 ohms/.sub.sq.
Inhibiting the achievement of better IR reflection (i.e. decreased "E" values) was the generally held belief that if the thickness of silver were increased to achieve higher IR reflectance (and thus lower "E" values) at least one or more of the following four detrimental affects would occur: (1) there would result a loss of durability; (2) the ultimate product would be too highly reflective, and thus become mirror-like; (3) the color would be driven to an unacceptably high purple or red/blue appearance; and/or (4) visible transmittance would become unacceptably low.
Durability, both mechanical and chemical, is an important factor to achieve in architectural glass generally whether used as a monolithic sheet or, for example, when used in an IG unit. As aforesaid, the handling, assembling and sealing of IG units places a premium on mechanical durability, while the need to edge seal the panes to create an insulating chamber therebetween creates the need for chemical durability due primarily to the nature of the sealant which inevitably contacts the coating. Aesthetically, both mirror-like and purple color qualities may eliminate the marketability of any product exhibiting these characteristics. Loss of visible transmittance while undesirable, does not become truly objectionable until, in a monolithic sheet, it drops below about 70% and in an IG unit it drops below about 63%. However, in certain uses, particularly where low shading coefficients (i.e. less than about 0.6) are desired, transmittance may actually be too high, even though emissivity is reasonably low. Generally speaking, where shading qualities are desired (i.e. to lower air conditioning costs), monolithic visible transmittance should be kept below 75% and preferably below 73%, while in a typical IG unit transmittance should be about 65% to 68%.
In partial confirmation of the above beliefs, is the rather complex layer system disclosed in U.S. Pat. No. 5,302,449 as well as its presumed commercial counterpart in IG unit form, known as Cardinal 171 sold by Cardinal IG Company. The layer system as taught in this patent varies the thicknesses and types of materials in the layer stack to achieve certain solar management qualities, as well as employing an overcoat of an oxide of zinc, tin, indium, bismuth, or oxides of their alloys including the oxide of zinc stannate, to achieve abrasion resistance. In addition, the system employs one or two layers of gold, copper or silver to achieve its end results. When two layers of silver are used it is said that the first is between 100 .ANG.-150 .ANG. and preferably about 125 .ANG. in thickness while the second, based thereon, is to be between 125 .ANG.-175 .ANG.. When only one silver layer is employed, it is taught that its thickness is to be about 100 .ANG.-175 .ANG., and preferably 140 .ANG.. Nowhere does this patent disclose the use of nickel or nichrome, nor the use of silicon nitride as an element(s) in the stack arrangement.
In actual commercial practice, the aforesaid Cardinal IG units have been found to achieve quite acceptable solar management properties including acceptable color characteristics and relatively good non-mirror-like visible reflectance (an example is reported hereinbelow for comparison). However, this otherwise quite acceptable system has been found lacking in chemical durability, and, as defined herein, may be said to lack chemical durability since it fails the prescribed boil test. While the precise reason for this is not known, the simple conclusion is that, as has been indicative of the prior art, sacrifices had to be made in at least one desirable characteristic, in order to achieve desirable levels of the others. In addition, due to the nature of the stack and elements used, the system is quite expensive to produce prinicipally due to the number and thickness of the layers required to achieve the desired result.
In the "BACKGROUND" section of the aforesaid '718 patent there is disclosed a further prior art architectural glass layer system which commercially has become known as Super-E III, a product of the Airco Corporation. This system, from the glass outwardly consists of the following layer stack: EQU Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4
It has been found in practice that in this Super-E III system the Ni:Cr alloy is 80/20 by weight Ni/Cr, respectively (i.e. nichrome), the two nichrome layers are reported as being 7 .ANG. thick, the Ag layer is specified as being only about 70 .ANG. thick except that it is stated that the silver may be about 100 .ANG. thick!, and the Si.sub.3 N.sub.4 layers are relatively thicker (e.g. 320 .ANG. for the undercoat and about 450 .ANG. for the overcoat). In reality, because of its thinness (i.e. about 70 .ANG.), the silver (Ag) layer has been found, in practice, to actually be rather semi-continuous in nature.
While this coating achieved good "durability" (i.e. the coating was scratch resistant, wear resistant and chemically stable) and thus achieved an important measure of this characteristic as compared to pyrolytic coatings, for glass at about 3 mm thick, E.sub.h is only about 0.20-0.22, and E. is about 0.14-0.17. Both of these emissivity values are rather high. In addition, sheet resistance (Rs) measures a relatively high 15.8 ohms/sq. (the more acceptable value being about 10.5 or less). Thus, while both mechanical and chemical durability are found to be quite acceptable and its monolithic sheet visible transmittance was a rather high 76.+-.1%, and while these coatings also proved to be compatible with conventional sealants used in IG units, its ability to handle IR radiation was less than desirable. In addition, its rather high monolithic visible transmittance of 76.+-.1% made such a system rather undesirable when lower shading characteristics were required.
Airco has followed its Super-E III system with what it has designated as its Super-E IV system. This system includes as its layer stack from the glass outwardly the following:
______________________________________ Element Thickness (.ANG.) ______________________________________ TiO.sub.2 Approx. 300 NiCrN.sub.x Approx. 8 Ag Approx. 105 NiCrN.sub.x Approx. 8 Si.sub.3 N.sub.4 Approx. 425 ______________________________________
This system is quite similar in performance to the Super-E III except that visible transmittance is higher (e.g. greater than 80%), emittance is lower (e.g. less than about 0.10) and shading coefficient is significantly higher (e.g. approx. 0.80). In addition, due to the use of TiO.sub.2 as an undercoat, the system is expensive to produce.
In addition to this Super-E III layer system, other coatings containing silver and/or Ni:Cr as layers for infrared reflectance and other light management purposes have been reported in the patent and scientific literature. See, for example, the Fabry-Perot filters and other prior art coatings and techniques disclosed in U.S. Pat. Nos. 3,682,528 and 4,799,745 (and the prior art discussed and/or cited therein). See also the dielectric, metal sandwiches created in numerous patents including, for example, U.S. Pat. Nos. 4,179,181; 3,698,946; 3,978,273; 3,901,997; and 3,889,026 just to name a few. While such other coatings have been known or reported, it is believed that prior to our invention, none of these prior art disclosures teach or have achieved the ability to employ the highly productive sputter-coating process and, at the same time, achieve an architectural glass which not only approaches or equals the durability of pyrolytic coatings, but which also achieves excellent solar management qualities as well.
In short, the above factors in the prior art would lead the skilled artisan directly away from any reasonable suggestion that a substantial thickening of the silver in a system such as the family of systems found in the '718 patent, coupled with an appropriate adjustment of the Si.sub.3 N.sub.4 thickness, could achieve a full range of desired characteristics particularly in the combined characteristics of: (1) acceptable, non-purple or non-red/blue colors; (2) non-mirror-like appearance, both inside and outside; (3) reasonably high transmittance values; (4) good mechanical durability; (5) superior chemical durability; and (6) exceptionally low emissivity values.
In view of the above, it is apparent that there exists a need in the art for a sputter-coated layer system which optimizes rather than unduly sacrifices on a perceived priority basis, the above-described characteristics for coated glass sheets generally, and IG units more particularly in an economical way. It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.